Many structures, such as residential homes and low rise buildings, are constructed on foundations that are not in direct contact with a stable load bearing underground stratum, such as, for example, bedrock. These foundations are typically concrete slabs or a footing upon which a foundation wall rests. The footing is generally wider than the foundation wall in order to distribute the structure's weight over a greater surface area of load bearing earth. Therefore, the stability of these structures depends upon the stability of the ground underneath or supporting the foundation. With time, the stability of the underlying soil may change for many reasons, such as changes in the water table, soil compaction, ground movement, or the like. When the stability of the support ground changes, many times the foundation will move or settle. The settling of a structure's foundation can cause structural damage reducing the value of the structure or total property.
For instance, structural settling can cause cracks in foundation walls. Unsightly cracks can appear on the interior or exterior of building walls and floors. In addition, settling can shift the structure causing windows and doors to operate poorly. Inventors have recognized the foundation-settling problem and have developed various devices and methods to correct its effects.
One common device and method to correct foundation settling consists of employing hydraulic jacks in conjunction with piers to lift the foundation. Piers, also known as piles or pilings, are driven into the ground by hydraulic mechanisms until the pier reaches bedrock or until the pier's frictional resistance equals the compression weight of the structure. Once these piers are secured in a stable underground stratum or several stable underground strata, further lifting by the hydraulic jacks raises the level of the foundation. When the foundation is raised to the desired level, the piers are permanently secured to the foundation. The hydraulic jacks are then removed. This method of correcting the level of a foundation generally requires the excavation of a hole adjacent to or underneath the foundation in order to position and operate the lifting equipment.
Steel piers are well known and exist in many varieties. One common type of a pier is a straight steel pier that is driven down until it reaches bedrock or stable soil weight bearing layer. These straight steel piers are rammed straight down into the ground. Another style of pier known to the art is a helical pier. On the end of a long pier shaft is a large helix. This helix distributes the weight of the pier over a larger surface area of soil making it a highly desirable pier structure to use. Unlike straight piers that are driven straight through the earth, it is necessary to screw the helical piers into the earth through rotating the pier shaft.
The use of a screwed-in-helix with a steel shaft is very common in supporting the footings and foundations of structures. For instance, a plurality of helical piers are typically installed at structurally strategic positions along the footing or foundation of a structure. These piers are then anchored together and interconnected by setting them all within reinforced concrete. In other instances, a plurality of steel piers are installed at various angles with respect to the building. These piers are then tied together to the footing or foundation with re-enforcing bars or pin connections. These bars or pin connections are then encapsulated within concrete.
When the helical steel pier is installed to support a footing or foundation of an existing structure, the pier is installed at an angle with respect to the building in order to accommodate the mechanical equipment necessary to screw the helical pier into the earth. This angle causes the building to place a lateral force on the pier resulting in an eccentric loading. When the top of the pier extends above the bottom of the footing or foundation and the load is carried on the top of the pier shaft, the eccentricity of the load is unnecessarily extended and weakens the load bearing capacity of the pier.
A helical pier shaft is disclosed in U.S. Pat. No. 5,171,107. This patent teaches a method wherein a helical anchor is screwed down into the earth. Importantly, this patent teaches that the helical anchor extends above the footing of the building. In addition, this patent teaches that the helical anchor extends off to the side of the footing creating an eccentric loading condition. Ideally, only vertical forces will exist in the final helical pier and foundation structure. However, because the pier taught by this patent extends to the side of the footing, the foundation places a lateral force against the pier that tends to push the pier outwardly. Through this lateral force that causes an eccentric loading the building shifts laterally over the pier until the pier no longer supports the vertical weight of the building. Consequently the pier's effectiveness is neutralized and the building subsides. It is highly desirable to design a pier that reduces the degree of this eccentric loading to prevent the lateral movement of the helical pier and footing or foundation.
Further, U.S. Pat. No. 5,171,107 teaches that a bracket assembly is needed to secure the helical pier to the footing. This bracket assembly requires a costly preparation of the footing. The bottom surface of building footers is typically very rough due to the manner in constructing the footer. In order to attach the bracket for the helical pier to the bottom surface of the footer, it is necessary to prepare the footer. Otherwise, if the pier bracket is placed against the uneven surface, stress fractures will occur in the footing damaging the structure and retarding the ability of the helical pier to support the building.
Preparing the footer is a labor intensive process that requires the use of concrete chippers or saws. These mechanical devices are used by laborers to smooth the bottom surface of the footer. It is therefore highly desirable to develop a pier system that can eliminate this costly and time consuming process. In addition, the bracket assembly is a complicated piece of equipment that greatly adds to the cost of the helical pier.
There are other foundation support technologies known to the art. For instance, Ortiz, U.S. Pat. No. 5,492,437, teaches a lifting device that is made of one or more power cylinders that are pivotally linked to a pier and to a foundation bracket assembly. The pivotal linkage results in self-alignment between the longitudinal axis of the pier and the axis along which compressive pressure is applied to the pier. This patent requires the pier to be lifted above the bracket in order to position the pier within the bracket.
West et al., U.S. Pat. No. 5,246,311, discloses a pier driver having a pair of opposing first upright members straddling a pier support. The upright members are temporarily attached to the foundation and a pair of opposing first foot members operably extending beneath the foundation. A plurality of secondary lifting mechanisms, in cooperation with the piers previously installed by the pier driver, are adapted to lift the foundation. The pier supports of the pier heads are then permanently fixed to the respective piers with a bracket to provide permanent support to the foundation. This patent requires the pier to be lifted above the bracket in order to position the pier within the bracket.
Bellemare, U.S. Pat. No. 5,253,958, describes a device for driving stakes into the ground, particularly a foundation stake used for stabilizing, raising, and shoring foundations. The device disclosed has two rods secured to two hydraulic jacks, the hydraulic jacks and the rods being parallel to the driving axis of the stake. A driving member with a hammering head is provided to drive the stake into the ground. This patent requires that the pier to be lifted above the bracket in order to position the pier within the bracket.
Despite these known designs, there is a very distinct need in the art to develop an improved pier design that reduces the amount of eccentric loading on the pier to reduce the lateral movement of the footing or foundation. Still further, there is a great need in the art to develop a pier that eliminates the costly bracket assembly.